Stainless steel alloy of high hardness



United States Patent 2,920,954 STAINLESS STEEL ALLOY OF HIGH HARDNESS Norman S. Mott, Westfield, NJ., assignor to Cooper Al- }oy Corporation, Hillside, N.J., a corporation of New ersey No Drawing. Application April 15, 1958 Serial No. 728,556

9 Claims. (Cl. 75-128) excellent corrosion-resistance of the well-known A181 316 and 317 types of stainless steel.

The new alloy is based on the simultaneous use of columbium and an increased amount of silicon. If desired, the nitrogen content also may be increased, as hereinafter explained, but this is optional and is unimportant compared to the use of columbium and increased silicon.

The broad range of my alloy includes the following chemical composition:

Percent C .08 Cr 18-30 Ni 8-12 Mo 2-6 Si 3-6 Cb 0.50-1.50 N 2 0.04-0.25

1 Maximum. Optional.

In respect to nitrogen a normal minimum residual is considered to be 0.04%. Therefore, at the minimum there is no intentional addition of nitrogen.

A closer and more preferred range is as follows:

Percent C .08 Cr 18-21 Ni 8-12 M0 3.75-4.25 Si 3.5-5.0 Cb 0.75-1.25 N, 2 0.04-0.1s

1 Maximum. Optional.

In both of the chemical composition ranges given above, the balance would be iron, manganese, sulfur, phosphorus and other elements incidental to manufacture and normally found as residuals in stainless steel alloys.

Four specific examples of my alloy are given in the following table:

1 Not intentionally added.

In the above and in all following tables BHN means Brinell hardness number; WQ means water quenched from 2000 F.; and PH means precipitation hardened by holding at 850-925 F. for eight hours, and then furnace cooling.

It will be noted that the above specific examples of my alloy all have a remarkable hardness of over 500 BHN in the PH condition. I

To show the eifect of adding columbium, the following table may be referred to. The test number X-18DF is repeated from Table I.

Table II Test No. X-18 X-18DA X-l8DB X-18DF The elements other than columbium are substantially constant. This table shows that increasing the columbium percentage increases the hardness at a substantially constant level of the other elements. I consider a BHN of 400 in the PH condition the lowest hardness desirable for the present objective, and I consider a BHN of 500 preferable. A BHN of 600 is an upper limit of hardness, because above that cracks are produced. Accordingly, a range of 0.50 to 1.50% columbium is indicated, while a more preferred or narrower range would be 0.75 to 1.25% for the columbium. It may be noted that in these tests the silicon was approximately 3.50%. Incidentally, test X-l8DB could have been included in Table I as showing a fifth example of my invention.

The effect of increasing the nitrogen content is shown in the following table:

The eifect of increasing siliconis shown in the following table: 7

a Table IV Test No. X-ISDA x-rsno X-ISDB X-ISD .percent 049 056 052 058 or" d 20. 2s 20. 0s 20. 10 20. 35 Ni ..d0 8.34 8.56 8;60 s. 60 Mn. .81 .88 .89 .83 Mo. (1 3.89 a. 92 r 3.96 3.78 si 3. 51 4. s9 3. 55 4. 97 0b-- .51 .54 .98 .86 2 .039 .043 .040 041 BHN WQ 286 351 302 387 BHN PH 418 512 495 555 The first two tests are with a low level' of columbium, while the second two are with a high level of columbium. Otherwise, the elements are unchanged, except for silicon, which is changed from about 3.5 to 5.0%.

' This table showsthe effect of increasing silicon on the BHN hardness values. Since a BHN of 400 minimum is my objective, it will be seen that a silicon content of about 3.5% is necessary at the lower columbium level of about 0.5%. A silicon content of about 3% is necessary at the higher columbium level of about 1.0%. Above 5% silicon, embrittlement and a tendency towards cracking sets in, and I have therefore set a maximum of 6%, with a preferred limit of 5%, for this element.

In all of the foregoing analyses, the iron content is not included, but it is understood that the balance is iron, subject to the presence of small amounts of impurities incidental to the usual melting practice when dealing with ferrous metals. The maximum carbon content should be no higher than say 0.08%

It will be understood that the alloys are fully resistant to the usual corrosion tests, specifically 65% boiling nitric acid, 50% sulphuric acid at 80 F., and 5% hydrochloric acid at 80 F. These alloys are also fully resistant to salt spray. As previously indicated, in this respect the present alloys, despite their very high hardness, are comparable to the well-known AISI 316 and 317 types of stainless steel.

The alloys are weldable by using welding rods of the same general composition as the alloy being welded. These alloys are soft enough in the quench-annealed condition to be readily machinable, and they may be precipitation hardened by a comparatively low-temperature heattreatment to a very high degree of hardness.

It will be apparent that while I have set forth specific examples of my improved alloys, changes may be made without departing from the scope of the invention as sought to be defined in the following claims.

I claim:

i 1. A precipitation hardenable stainless steel alloy of very high hardness having a hardness exceeding 400 BHN in the precipitation hardened state, said alloy having 'a range of 18% to 30% chromium, 8% to 12% nickel, 2%

1.5% columbium, and a carbon content not exceeding 0.08%, the remainder being essentially iron, with manganese, sulphur, phosphorus, and other elements incidental to manufacture and normally found as residuals in stainless steel alloys, and an optional nitrogen content of 0.04% to 0.25%.

3. A precipitation hardenable stainless steel alloy of very high hardness having a hardness exceeding 400 BHN in the precipitation hardened state, said alloy having a range of 18% to 21% chromium, 8% to 12% nickel, 3.75% to 4.25% molybdenum, 3.5% to 5.0% silicon, 0.75% to 1.25% columbium, and a carbon content not exceeding 0.08%, the remainder being essentially iron,

4. A precipitation hardenable stainless steel alloy of Veryhigh hardness having a hardness exceeding 400 BHN in the precipitation hardened state, said alloy having a range of 18% to 21% chromium, 8% to 12% nickel, 3.75% to 4.25% molybdenum, 3.5% to 5.0% silicon, 0.75% to 1.25% columbium, and a carbon content not exceeding 0.08%, the remainder being essentially iron, with manganese, sulphur, phosphorus, and other elements incidental to manufacture and normally found as residuals in stainless steel alloys, and an optional nitrogen content of 0.04% to 0.15%. V

5. A precipitation hardenable stainless steel alloy of very high hardness having a hardness exceeding 400 BHN in the precipitation hardened state, said alloy having approximately 20.08% chromium, 8.56% nickel, 0.88% manganese, 3.92% molybdenum, 4.89% silicon, 0.54% columbium, 0.043% nitrogen, and 0.056% carbon, the remainder being essentially iron and other elements incidental tov manufacture and normally found as residuals in stainless steel alloys.

6. A precipitation hardenable stainless steel alloy of very high hardness having a hardness exceeding 400 BHN in the precipitation hardened state, said alloy having approximately 20.21% chromium, 8.81% nickel, 0.79% manganese, 3.76% molybdenum, 3.49% silicon, 0.96%

.columbium, 0.12% nitrogen, and 0.053% carbon, the

- very high hardness having a hardness exceeding 400 BHN in the precipitation hardened state, said alloy having approximately 20.35% chromium, 8.6% nickel, 0.83% manganese, 3.78% molybdenum, 4.97% silicon, 0.86% columbium, 0.041% nitrogen, and 0.058% carbon, the remainder being essentially iron and other elements incidental to manufacture and normally found as residuals in stainless steel alloys.

8. A precipitation hardenable stainless steel alloy of very high hardness having a hardness exceeding 400 BHN in the precipitation hardened state, said alloy having approximately 20.01% chromium, 8.69% nickel, 0.85% manganese, 3.82% molybdenum, 3.56% silicon, 1.23% columbium, 0.041% nitrogen, and 0.049% carbon, the remainder being essentially iron and other elements incidental to manufacture and normally found as residuals in stainless steel alloys.

9. A precipitation hardenable stainless steel alloy having a hardness exceeding 400 BHN in the precipitation hardened state, said alloy having approximately 20.10% chromium, 8.60% nickel, 0.89% manganese, 3.96% molybdenum, 3.55% silicon, 0.98% columbium, 0.04% nitrogen, and 0.052% carbon, the remainder being essentially iron and other elements incidental to manufacture and normally found as residuals in stainless steel alloys.

References Cited in the file of this patent UNITED. STATES PATENTS 

1. A PRECIPITATION HARDENABLE STAINLESS STELL ALLOY OF VERY HIGH HARDNESS HAVING A HARDNESS EXCEEDING 400 BHN IN THE PRECIPITATION HARDENED STATE, SAID ALLOY HAVING A RANGE OF 18% TO 30% CHROMIUM, 8% TO 12% NICKEL, 2% TO 6% MOLYBDENUM, 3% TO 6% SILICON, 0.5% TO 1.5% COLUMBIUM, AND A CARBON CONTENT NOT EXCEEDING 0.08% THE REMAINDER BEING ESSENTIALLY IRON. 